On Pseudorandom Encodings

Abstract

We initiate a study of pseudorandom encodings: efficiently computable and decodable encoding functions that map messages from a given distribution to a random-looking distribution. For instance, every distribution that can be perfectly and efficiently compressed admits such a pseudorandom encoding. Pseudorandom encodings are motivated by a variety of cryptographic applications, including password-authenticated key exchange, "honey encryption" and steganography.The main question we ask is whether every efficiently samplable distribution admits a pseudorandom encoding. Under different cryptographic assumptions, we obtain positive and negative answers for different flavors of pseudorandom encodings, and relate this question to problems in other areas of cryptography. In particular, by establishing a twoway relation between pseudorandom encoding schemes and efficient invertible sampling algorithms, we reveal a connection between adaptively secure multiparty computation for randomized functionalities and questions in the domain of steganography.

Using data compression and randomization to build an unconditionally secure short key cipher

“…Moreover, homophonic coding can be used to compress and randomize together [11], [12]. The goal of both transformations is to make the probability distribution of the original messages closer to the uniform one (see an overview in [13]). Interestingly, both transformations have been successfully applied to some cryptographic problems: they were used to extract randomness [14]- [16] and to build an ideal steganographic system [17].…”